1. Field of the Invention
The present invention relates to a constant flow valve and a constant flow mixing method for mixing a plurality of fluids using the constant flow valves.
2. Description of the Related Art
In the past, as a constant flow valve used for supply of a fluid at a constant flow, broad use has been made of ones which lead part of a secondary pressure side fluid into a control chamber having a valve member and use this as pilot pressure for making the flow of supply constant. In this constant flow valve, however, the fluid remains stagnant in the pipe laid for the pilot pressure (pilot pipe) and becomes so-called xe2x80x9cdead waterxe2x80x9d. This breeds bacteria which sometimes flows into the main flow. To solve this problem, for example, a constant flow valve of a full flow replacement type not using a pilot pipe has been proposed as described in Japanese Unexamined Patent Publication (Kokai) No. 6-123371.
The constant flow valve 90 shown in FIG. 6 relates to the structure disclosed in the above publication. A chamber 100 is divided by a pressure receiving member 120 biased by a spring member 121 into a primary side (lower half) chamber 101 and a secondary side (upper half) chamber 102. A controlled fluid flows in from an inlet port 103 of the primary side chamber 101 and flows out from an outlet port 104 of the primary side chamber 101, passes through a connecting pipe 130 provided with a flow regulating valve 131, flows from an inlet port 105 of the secondary side chamber 102 into the secondary side chamber 102, and flows out from an outlet port 106. In the primary side chamber 101, a valve chamber 110 is provided. A valve member 112 biased by a spring member 113 adjusts the opening degree of a valve seat 111 in accordance with the amount of action of the pressure receiving member 120. Reference numeral 115 is a through hole formed in the valve member 112.
According to this constant flow valve 90, as will be understood from the different states of the left and right in the figure, when the pressure of the primary side or secondary side changes, the pressure receiving member 120 actuates due to the differential pressure of the primary side fluid and secondary side fluid as a whole. In accordance with that amount of action, the valve member 112 of the valve chamber 110 of the primary side fluid moves, whereby the flow rate of the primary fluid is adjusted to a predetermined rate by the adjustment of the opening degree of the valve seat 111. Since no pilot pipe is used, fluid does not remain stagnant and no dead water is produced as explained above.
In this constant flow valve 90, as illustrated, spring members 121 and 113 are provided for biasing the pressure receiving member 120 and valve member 112. The fluid contacts the spring members 121 and 113, so when the fluid has metal corrosiveness or is an organic solvent, electrolyte, gas, etc., the springs 121 and 113 are liable to be corroded or contaminated by impurities. The valve cannot be used in lines not permitting chemicals and other impurities.
Further, in this constant flow valve 90, since the spring members 121 and 113 are built into the portion contacting the fluid inside the device, there is the structural problem that the differential pressure cannot be changed from the outside. Further, this configuration does not consider the pressure receiving member 120 or the pressure receiving area of the valve member 113, so complete maintenance of a constant differential pressure is difficult. The problem has been pointed out that when the resistance due to the restrictor is large, the flow rate is controlled relatively accurately, but when the resistance is small and the differential pressure is low, the valve cannot function effectively for fluctuations in pressure at the primary side and secondary side.